Crosstalk between membrane receptors and nuclear hormone receptors increasingly is recognized as a physiological strategy used by several cell systems. As a pleiotropic regulator of the pituitary gonadotropes, the hypothalamic hormone, gonadotropin releasing hormone (GnRH) and its receptor (a G-protein coupled receptor) utilize multiple signaling systems. One result of GnRH-receptor activation is GnRH self-priming, which is manifested as potentiation of the luteinizing hormone (LH) secretory response to a subsequent challenge of GnRH. The consequence of GnRH self-priming is signal amplification, which is crucial for ensuring the explosive release of LH responsible for ovulation. We have shown that all characteristics of GnRH self-priming are shared by progesterone in its augmentation of GnRH-stimulated secretion and that GnRH is able to stimulate transcription of a reporter gene carrying progesterone response elements in gonadotropes containing endogenous progesterone receptors (PR). Hypothesis: self-priming is a result of a GnRH signaling pathway that culminates in ligand-independent activation of the PR and targeted gene expression. The long-term goals of this proposal are to determine the mechanistic basis for the crosstalk and to identify the post-transcriptional events responsible for augmentation/priming of LH secretion. For aim 1, we will determine the upstream signaling components that intervene between the GnRH-receptor activation and PR activation. The focus for aim 2 is the significance of the PR-A and PR-B isoforms in the crosstalk pathway. Specifically, we will establish the relative expression of the PR-A and PR-B mRNA and protein in rat compared to mouse gonadotropes and determine the relative roles for the PR isoforms in the GnRH-priming and progesterone augmentation process. In aim 3, we will identify the changes in the mRNA expression pattern associated with GnRH self-priming in single gonadotropes. We reason that, if there is convergence at the PR, there should be overlap in a subset of genes activated either by GnRH or progesterone. Cell models will be cultured gonadotropes from rats and wild-type and PR-knockout (PRKO) mice and the LbetaT2 gonadotrope cell line.